1,25(OH).sub.2 D.sub.3 and Analogs
The 1.alpha.-hydroxylated metabolites of vitamin D--most importantly 1.alpha.,25-dihydroxyvitamin D.sub.3 and 1.alpha.,25-dihydroxyvitamin D.sub.2 --are known as highly potent regulators of calcium homeostasis in animals and humans. More recently, their activity in cellular differentiation has also been established. As a consequence, many structural analogs of these metabolites, such as compounds with different side-chain structures, different hydroxylation patterns, or different stereochemistry, have been prepared and tested. Important examples of such analogs are 1.alpha.-hydroxyvitamin D.sub.3, 1.alpha.-hydroxyvitamin D.sub.2, various side-chain fluorinated derivatives of 1.alpha.,25-dihydroxyvitamin D.sub.3, and side-chain homologated analogs. Several of these known compounds exhibit highly potent activity in vivo or in vitro, and possess advantageous activity profiles and thus are in use, or have been proposed for use, in the treatment of a variety of diseases such as renal osteodystrophy, vitamin D-resistant rickets, osteoporosis, psoriasis, multiple sclerosis, and certain malignancies.
1,25-(OH).sub.2 D.sub.3 as an Immunomodulator
The first indication that vitamin D might modulate immunity was the discovery that peripheral blood monocytes and activated T lymphocytes have 1,25-dihydroxyvitamin D.sub.3 receptors (reviewed in Manolagas, S. C., et al., Mol. and Cell. Endocrin. 43:113-122, 1985). Despite many investigations, 1,25-dihydroxyvitamin D.sub.3 immunomodulatory activity remains largely undefined and often controversial (reviewed in Manolagas, S. C., et al., supra, 1985; Rigby, W. F. C., Today 9:54-57, 1988; and Lemire, J. M., et al., J. Nutr. 125:1704S-1708S, 1995).
The action of 1,25-dihydroxyvitamin D.sub.3 on human peripheral blood mononuclear cells (PBMC) has been studied extensively in vitro. These in vitro experiments showed that the hormone inhibited mitogen-stimulated proliferation of the PBMC (Lemire, J. M., et al., J. Clin. Invest. 74:657-661, 1984; Rigby, W. F. C., et al., J. Clin. Invest. 74:1451-1455, 1984) by reducing IL-2 production (Lemire, J. M., et al., J. Immunol. 134:3032, 1985; Iho, S., et al., Immunol. Let. 11:331-336, 1985; Manolagas, S. C., et al., J. Clin. Endocrinol. Met. 63:394, 1986) at the level of gene transcription (Alroy, I., et al., Mol. Cell. Biol. 15:5789-5799, 1995). In contrast, Bhalla, et al. (Bhalla, A. K., et al., J. Immunol. 133:1748-54, 1984) reported that the hormone did not inhibit mitogen-stimulated mouse spleen and thymus cell proliferation, although it did inhibit antigen-stimulated proliferation of these cells. Lacey, et al. (Lacey, D. L., et al., J. Immunol. 138:1680-1686, 1987) reported that the hormone actually stimulated mitogen-induced proliferation of cloned mouse T-cells. No studies have directly addressed the action of the hormone on T lymphocyte differentiation and function in vivo.
Disparate results have been reported for T lymphocyte IFN-.gamma. synthesis in vitro. Rigby, et al. (Rigby, W. F. C., et al., J. Clin. Invest. 79:1659-1664, 1987) and Reichel, et al. (Reichel, H., et al., Proc. Natl. Acad. Sci. USA 84:3387-3389, 1987) showed that 1,25-dihydroxyvitamin D.sub.3 decreased IFN-.gamma. synthesis in mitogen-stimulated PBMC. However, Muller, et al. (Muller, K., et al., Immunol. Let. 35:177-182, 1993) reported that the hormone had no effect on IFN-.gamma. synthesis in human T-cell lines. The hormone inhibited cytotoxic T lymphocyte development but not cytotoxic function (Merino, F., et al., Cell. Immunol. 118:328-336, 1989).
There is controversy about 1,25-dihydroxyvitamin D.sub.3 action on monocyte/macrophage cells in vitro. 1,25-dihydroxyvitamin D.sub.3 enhanced a myeloid leukemia cell's differentiation to the macrophage phenotype (Manolagas, S. C., et al., supra, 1985). It also increased monocyte/macrophage production of M-CSF, TNF-.alpha., and prostaglandin E2, but decreased IL-12 synthesis (Lemire, J. M., et al., FASEB J. 8:A745 (abs), 1994). The hormone decreased macrophage costimulatory function for T-cell proliferation (Rigby, W. F. C. and M. G. Waugh, Arthritis Rheum. 35:110-119, 1992). Disparate results have been reported for 1,25-dihydroxyvitamin D.sub.3 effects on IL-1 synthesis in vitro. The hormone decreased IL-1 synthesis in some reports (Iho, S., et al., supra, 1985; Tsoukas, C. S., et al., J. Clin. Endocrinol. Metab. 69:127-133, 1989) and increased IL-1 synthesis in other reports (Amento, E. P., J. Clin. Invest. 73:731-739, 1987; Bhalla, A. K., et al., Immunol. 72:61-64, 1991; Fagan, D. L., et al., Mol. Endocrinol. 5:179-186, 1991). Likewise, some investigators reported that 1,25-dihydroxyvitamin D.sub.3 enhanced class II protein expression in vitro (Morel, P. A., et al., J. Immunol. 136:2181-2186, 1986) but others reported that it decreased class II protein expression (Amento, E. P., supra, 1987; Carrington, M. N., et al., J. Immunol. 140:4013-4018, 1988; Rigby, W. F. C., et al., Blood 76:189-197, 1990). Together these findings provide no clear and consistent view of how 1,25-dihydroxyvitamin D.sub.3 might modify macrophage function. No studies have directly addressed the action of the hormone on monocyte/macrophage differentiation and function in vivo.
There is also controversy about 1,25-dihydroxyvitamin D.sub.3 action on B lymphocytes (reviewed in Rigby, W. F. C., supra, 1988). Lemire, et al. (Lemire, J. M., et al., supra, 1984) reported that the hormone inhibited mitogen-stimulated IgG and IgM synthesis by human peripheral blood mononuclear cells. Suppressive and enhancing effects of 1,25-dihydroxyvitamin D.sub.3 on mitogen-stimulated B cell proliferation and on antibody synthesis in vitro have been shown. In vivo, 1,25-dihydroxyvitamin D.sub.3 has been reported to enhance antibody synthesis in some studies (Abe, J., et al., Endocrinology 124:2645-2647, 1989; Ross, T. K., et al., Vitamins Hormones 49:281-326, 1994; Daynes, R. A., et al., Infec. Immun. 64:1100-1109, 1996) and to inhibit it in other studies (Lemire, J. M., et al., supra, 1995).
Lemire, et al., Transplantation 54:762-763, 1992 have described prolongation from 7 to 16 days of the survival of murine cardiac allografts by the vitamin D.sub.3 analog 1,25-dihydroxy-delta 16-cholecalciferol. The effective dose of this analog caused severe hypercalcemia. Other analogs showed some prolongation, but also caused hypercalcemia.
Johnsson, et al., Transplant. Proc. 28:888-891, 1996 30 described prolongation of survival from 3 to 14 days by administration of the vitamin D analog MC 1288 in Wistar/Kyoto rat cardiac allografts. These workers concluded that the analog worked best in combination with cyclosporin. The analog increased survival from 8-11 days but also induced hypercalcemia.
1,25-dihydroxyvitamin D.sub.3 (1,25(OH).sub.2 D.sub.3) treatment have been tested by others for their ability to prolong experimental transplanted cardiac graft survival. Lemire, et al., supra, 1992 used the murine cardiac graft model and showed that 1,25(OH).sub.2 D.sub.3 did not prolong graft survival. In a review, Bouillon (Bouillon, et al., Endocrine Review 16 [2] 200-257, 1995) cites one experiment in the rat where cardiac grafts were prolonged briefly with 1,25(OH).sub.2 D.sub.3 treatments (6 control days versus 10 treated days). The dose of 1,25(OH).sub.2 D.sub.3 necessary for this minimal graft prolongation was 500 ng/kg/day given intraperitoneally. The overall conclusion from these experiments was that unmodified 1,25(OH).sub.2 D.sub.3 alone does not prolong graft survival.